Some connection systems between electronic components such as printed circuit boards (PCBs), backplanes, cables, integrated circuits (ICs), IC connectors and the like, use metal pins and metallic, plated-through cylinders called vias. Often, such a system includes one electronic component which has a set of metal pins and another component which has a corresponding set of vias. In general, the component with the pins includes a housing which positions the pins such that the pins extend from the housing in a grid-like manner (e.g., in rows and columns). Similarly, the component with the vias typically arranges the vias in a complementary manner such that holes of the vias align with ends of the pins when the two components are brought into alignment with one another.
In general, to connect the two components, the housing of the pin-providing component is positioned relative to the via-providing component such that the end of each pin properly aligns with a corresponding via hole. Then, the housing of the pin-providing component and the via-providing component are brought together so that the metal pins evenly insert into the via holes. There are different conventional approaches to making sure that the connections between the pins and the vias are secure.
One conventional approach is called xe2x80x9creflow solderingxe2x80x9d or the xe2x80x9cwave solderingxe2x80x9d. In this approach, wave soldering machinery typically solders the pins and vias together once the pins have been inserted into the vias. In general, molten solder flows through the remaining voids between the pins and the vias to form electrical pathways for carrying signals between the pins and the vias.
Typically, the reflow approach uses a grid pattern pitch of approximately 0.100 of an inch or 0.100xe2x80x3 (often pronounced xe2x80x9c100 milsxe2x80x9d). That is, the pins are arranged generally in rows and columns such that the center axis of each pin is approximately 0.100xe2x80x3 away from the center axes of pins in adjacent rows and columns. Similarly, the vias typically are arranged in complementary rows and columns such that the center axis of each via is approximately 0.100xe2x80x3 away from the center axes of vias in adjacent rows and columns.
For the reflow soldering approach, the diameters of the holes of the vias typically are 100% larger than the maximum cross-sectional dimension of the pins in order to promote solder flow within the vias once the pins have been inserted. For example, for a round pin having a maximum diameter of 0.030xe2x80x3, the inner diameter of the via hole is generally 0.060xe2x80x3.
In general, pins having a square cross-section, which are stamped from flat metal stock, are also suitable for use in the reflow soldering approach. Such square cross-sectioned shaped pins generally are less expensive than pins having a circular cross-section or pins with rounded corners since the square cross-sectioned pins typically do not need to undergo a tumbling, coining or turning process to round the corners of the pins. Rather, the pin manufacture can simply cut/punch/stamp the square cross-sectioned pins from a sheet of metal stock. Accordingly, the thickness of each pin is essentially the width of the metal stock. Although flat pins are less expensive than rounded pins, better soldering results typically are obtained with pins having circular cross-sections or rounded corners than with pins having a square or rectangular cross-section and sharp corners.
Another approach to forming secure connections is the xe2x80x9cintrusive reflow solderingxe2x80x9d approach. In this approach, automated equipment typically provides portions of solder and flux for each pin/via combination prior to insertion of the pins into the via holes. Often, the equipment partially inserts these solder portions (sometimes in the form of a paste and sometimes as solder pre-forms assembled to the pin base) into the via holes of a component prior to pin insertion. Then, the equipment brings the pin-providing component and the via-providing component together by inserting the pins of the pin-providing component into the via holes of the via-providing component. The equipment then provides heat to melt the solder portions and additional solder to fill any remaining voids between the pins and the vias.
Typically, the grid pattern for the intrusive reflow approach has a pitch that is similar to that used in the reflow soldering approach (i.e., 0.100xe2x80x3), or a finer pitch in the range of 0.080xe2x80x3 to 0.100xe2x80x3. Furthermore, for the intrusive reflow soldering approach, the diameters of the vias holes typically are not 100% larger than the maximum cross-sectional dimension of the pins, as in the reflow soldering approach. Rather, the via holes for the intrusive reflow approach generally can be 25% larger than the maximum cross-sectional dimension of the pins for sufficient solder distribution since pre-placement of the solder portions facilitates solder delivery into the via holes.
For the intrusive reflow soldering approach, as in the reflow soldering approach, square or round cross-sectioned pins are generally preferred. Pins having a round cross-section are ideally suited for intrusive reflow soldering. Pins having a square cross-section are generally suitable but require more solder. Pins having a rectangular (but non-square) cross-section typically are not used in the reflow soldering approach since such pins provide little or no additional benefit over pins having a square cross-section.
Another approach to forming secure connections between two components is called the xe2x80x9ccompression fitxe2x80x9d approach. This approach is also known as the xe2x80x9ccompliant fitxe2x80x9d or the xe2x80x9ceye-of-the-needlexe2x80x9d approach. In this approach, no solder is used. Rather, each pin typically is flat (i.e., each pin has a square or rectangular cross-section) and has a hole (or eye) stamped through it (i.e., the xe2x80x9ceye-of-the-needlexe2x80x9d) allowing the pin to compress when inserted into a via to form a secure connection. In particular, each pin has a cross-sectional diameter that is sized to be larger than the cross-section diameter of its corresponding via hole to provide an interference fit when inserted into that via hole. Accordingly, when the pins are inserted into the holes of the vias, the pins compress to fit within the via holes and apply pressure against the inner metallic surfaces of the vias (e.g., copper-plated surfaces). As a result, the connections formed between the pins and vias are secure.
Typically, the compression fit approach uses a finer grid pattern pitch than either the reflow soldering approach or the intrusive reflow soldering approach. One example of a pitch that is suitable for the compression fit approach is an 0.080xe2x80x3 by 0.060xe2x80x3 grid. Connection systems which used grids of this size are often called xe2x80x9chigh-densityxe2x80x9d due to the large number of connections (i.e., pin/via connections) that can be formed in such a small area.
Typically, pins which have a rectangular or even square cross-section are used in the compression fit approach. The range for a typical width for a rectangular pin suitable for use in the compression fit approach is 0.012xe2x80x3 to 0.015xe2x80x3. The range for a typical pin length is 0.026xe2x80x3 to 0.028xe2x80x3. The sides of the compression-fit pin typically are allowed to vary by 0.002xe2x80x3 in either direction. A particular characteristic of compression fit pins is their central portions which have a bulging shape. That is, the shape of the eye and the pin material around the eye is designed to provide a particular form factor, and a particular size reduction when inserted into a via.
Unfortunately, there are disadvantages to the conventional reflow soldering, compression fit and intrusive reflow soldering approaches. For example, the conventional reflow soldering approach generally is not used in high-density connection applications (e.g., in connection arrangements having rows and columns less than 0.100xe2x80x3 apart) for several reasons. In particular, reflow soldering connection systems are susceptible to tail shorts, i.e., shorts formed by excess solder hanging from pin ends extending from adjacent via holes. Additionally, the via holes are typically sized to be 100% larger than the maximum pin diameters to promote solder flow within the via holes. This size restriction imposes a limit on how small the grid pattern pitch of the connection system can be before significantly increasing the likelihood of forming unwanted shorts between adjacent vias. Moreover, any reduction in the size of the via would tend to hinder solder flow around the standard reflow soldering pins thus creating excessive voids within the via holes which would pose manufacturing yield difficulties and product reliability issues. Furthermore, in a high-density configuration, solder, which occasionally flows or xe2x80x9cwicks upxe2x80x9d the lengths of the pins and flows out the ends of the via holes closest to the housing (e.g., a connector body) holding the pins, would be more likely to cause shorts directly beneath the housing. Such shorts may be hidden by the housing and inaccessible for detection and/or repair.
The compression fit approach suffers from manufacturing yield and reliability drawbacks as well. In particular, formation of high-density connections between compression fit pins and vias typically require high insertion forces (particularly compared to low or zero insertion force situations for reflow soldering pins and vias). Accordingly, a small abnormality (e.g., a bend or irregular shape which places a pin or via slightly out of tolerance) can cause the pin to collapse or bend improperly, or cause the via to distort. As a result, the electrical connection, if made at all, will likely be unreliable.
The intrusive reflow soldering approach also suffers from certain drawbacks. In particular, this approach is complex and expensive to implement. In particular, specialized procedures, equipment and soldering materials are required to pre-position solder at the via holes prior to pin insertion, insert the pins and then apply heat and additional solder to form secure connections between components. Some component manufacturers have been known to prefer the reflow soldering approach or the compression fit approach over the intrusive reflow soldering approach due to the added complexity and expense which typically characterizes the intrusive reflow soldering approach.
In contrast to the above-described conventional approaches, the invention is directed to techniques for forming a soldered connection using a pin having a channel. The channel enables the pin to form a secure connection with a via (e.g., by facilitating gas percolation out of the via hole during soldering to improve solder flow, by holding solder prior to pin insertion and soldering, or by facilitating accurate pin bending to hold solder or a pin insert member prior to pin insertion and soldering) to improve connection system reliability and increase manufacturing yields.
In one arrangement, the pin has a surface which includes (i) a first surface area, (ii) a second surface area that is substantially parallel to the first surface area, and (iii) a channel surface area which defines a channel that extends from the first surface area toward the second surface area. To form a soldered connection, the pin is inserted into a cavity defined by a via of a connecting member (e.g., a circuit board), in a direction that is parallel to a central axis of the via. The pin is then soldered to the via to establish an electrical pathway between the pin and the via. Depending on the particular arrangement (as will be explained in further detail below), the channel generally facilitates the introduction of solder into the cavity of the via. Accordingly, the cavity dimension of the via can be smaller than that required for vias of the conventional reflow soldering approach (i.e., less than 100% of the maximum pin cross-section as is typically required for the conventional reflow soldering approach). Hence, the invention is suitable for use in high-density, micro-soldered connection arrangements (e.g., in situations with vias closer together than in the conventional reflow soldering approach).
In one arrangement, the channel is a tunnel that extends from a first plane defined by the first surface area to a second plane defined by the second surface area through the pin. In this arrangement, the channel allows gas within the via hole to escape out of the remaining voids within the via cavity during soldering. Preferably, the pin is located relative to the via such that a portion of the channel extends outside the cavity defined by the via to facilitate gas percolation even when solder has almost filled the via cavity. Additionally, the channel provides additional surface area for drawing solder. In a preferred arrangement, a solder-stop member is placed around the pin such that a first portion of the channel extends on a first side of the solder-stop member and a second portion of the channel extend on a second side of the solder-stop member that is opposite the first side. Such an arrangement helps block solder such that it is less likely to escape out of the via cavity while continuing to enable gas to escape through the channel.
In this arrangement, the presence of the channel promotes solder flow within the via cavity to the extent that the via cavity can be made narrow (e.g., less than 100% of the maximum pin diameter as is typically used in a conventional reflow soldering approach). Accordingly, the via can be positioned closer to other neighboring vias in a high-density connection arrangement. Hence, the benefits of forming a soldered connection (e.g., high reliability and improved manufacturing yields) can be derived in a high-density, micro-soldered configuration.
In the above-described arrangement, the channel preferably extends along a central axis of the pin to facilitate gas percolation and to promote solder flow. In one arrangement, the channel extends all the way to the end of the pin to form a solder flow path. That is, the channel includes a gap at the end of the pin. Such a gap facilitates entry of the solder into the via cavity (and particularly the channel) during soldering.
In one arrangement, a portion of solder can be positioned within the channel prior to soldering. Accordingly, less solder is required to flow into the via hole during soldering. Preferably, the solder is fitted within the channel (e.g., by automated equipment) such that (i) a first portion of the piece of solder extends from the channel of the pin in a first direction, and (ii) a second portion of the piece of the solder extends from the channel of the pin in a second direction that is opposite the first direction. Preferably, the first and second portions are substantially the same amounts. Any amounts that interfere with pin insertion can be shaped prior to insertion to provide a minimal or zero insertion force fit.
In another arrangement, the first surface area defines a first plane, the second surface area defines a second plane that is parallel to the first plane, and the channel extends from the first plane toward the second plane to enable machinery (e.g., automated equipment) to bend the pin along the channel prior to insertion of the pin into the via hole. In this arrangement, the channel preferably forms a groove along one of the sides of the pin to facilitate accurate and controlled bending of the pin along the channel since no material needs to be displaced in the channel region during bending.
In one arrangement, the pin further includes multiple tab portions which bend around a pin insert member when the pin is bent. The multiple tab portions of the pin hold the pin insert member in place during soldering. The pin insert member is preferably metallic and contributes both structural strength and electrical conductivity to the connection formed between the pin and the via.
In another arrangement, the channel is a groove or slot which divides the pin into a first pin portion and a second pin portion. In this arrangement, the first and second pin portions are bent relative to each other such that the first and second pin portions hold a piece of solder for soldering. Accordingly, the piece of solder enters the via hole prior to soldering and less solder is required to flow into the via hole during soldering. Preferably, the surface of the pin further includes a first side-channel surface area that defines a first side-channel (in addition to the grooved-channel), and a second side-channel surface area that defines a second side-channel. In this arrangement, the first and second side-channels are essentially holes which extend along a direction that is parallel to the central axis of the via. Accordingly, gas can percolate out of the via hole through these multiple side-channels during soldering.
Preferably, the pin has a cross-section that is less than or equal to a cross-section of the cavity defined by the via. Accordingly, insertion of pin into the via hole requires little or no insertion force (e.g., xe2x80x9ca zero insertion force connection systemxe2x80x9d). This arrangement reduces the likelihood of bending the pin or distorting the via during pin insertion.
In the above-described arrangements of the invention, it should be understood that there is no restriction on the shape of the pin or its channel (as there is in the compression fit approach where a compression fit pin is designed to provide a particular cross-sectional reduction during insertion into a via). Accordingly, the top portion of the pin (or neck), which is adjacent the housing holding the pin, can be made thicker than compression fit pins to further prevent pin bending during pin insertion.
The features of the invention, as described above, may be employed in electronic systems and related components such as those manufactured by EMC Corporation of Hopkinton, Mass.